Connected: An Internet Encyclopedia
RFC 1661 - 5.7. Protocol-Reject

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### 5.7. Protocol-Reject

Description

  Reception of a PPP packet with an unknown Protocol field indicates that the peer is attempting to use a protocol which is unsupported. This usually occurs when the peer attempts to configure a new protocol. If the LCP automaton is in the Opened state, then this MUST be reported back to the peer by transmitting a Protocol-Reject.

  Upon reception of a Protocol-Reject, the implementation MUST stop sending packets of the indicated protocol at the earliest opportunity.

  Protocol-Reject packets can only be sent in the LCP Opened state. Protocol-Reject packets received in any state other than the LCP Opened state SHOULD be silently discarded.

A summary of the Protocol-Reject packet format is shown below. The fields are transmitted from left to right.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Code      |  Identifier   |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       Rejected-Protocol       |      Rejected-Information ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code

  8 for Protocol-Reject.

Identifier

  The Identifier field MUST be changed for each Protocol-Reject sent.

Rejected-Protocol

  The Rejected-Protocol field is two octets, and contains the PPP Protocol field of the packet which is being rejected.

Rejected-Information

  The Rejected-Information field contains a copy of the packet which is being rejected. It begins with the Information field, and does not include any Data Link Layer headers nor an FCS. The Rejected-Information MUST be truncated to comply with the peer's established MRU.

Next: 5.8. Echo-Request and Echo-Reply

Connected: An Internet Encyclopedia
RFC 1661 - 5.7. Protocol-Reject